WHO assistant director-general for health security Keiji Fukuda gestures on May 14, 2014 in Geneva during a press conference following a closed-door emergency talks on the deadly MERS virus, which has killed 142 people in Saudi Arabia and is sparking rising concern over an increasing number of cases elsewhere. AFP PHOTO / FABRICE COFFRINI

The UN health agency Wednesday warned countries to bolster their guard against the MERS virus, which has killed 152 people in Saudi Arabia and is causing alarm as it spreads elsewhere.

The World Health Organization said that a meeting of its emergency committee, which groups medical and policy experts from around the globe, had flagged a significant increase in concerns about the potentially fatal Middle East Respiratory Virus (MERS).

"The committee indicated that the seriousness of the situation had increased in terms of public health impact, but that there is no evidence of sustained human-to-human transmission," the WHO said.

The committee's concerns "centered on the recent sharp rise in cases, systemic weaknesses in infection prevention and control, as well as gaps in critical information, and possible exportation of cases to especially vulnerable countries," it added.

As a result, the health experts called on governments, notably in affected countries, to bolster policies for infection prevention and control, and ensure they are implemented in health-care facilities nationwide.

It also said there was more need to raise awareness of how to fight MERS across all arms of government and among the general public.

MERS causes fever, coughing and shortness of breath, and can be lethal particularly among older people and those with existing health problems.

Some 30 percent of the several hundred people infected with it have died, according to the US Centers for Disease Control and Prevention.

The virus first emerged in Saudi Arabia in 2012 and recent research has suggested it may originate in camels.

Since April 2012, 536 laboratory-confirmed cases have been reported officially to WHO.

The vast majority of cases have been in Saudi Arabia, and most of those elsewhere have involved people had travelled to the kingdom.

On Wednesday the Netherlands became the 13th country outside of Saudi Arabia to report a case of MERS. Since December there have also been confirmed or suspected cases since December in Egypt, Greece, Jordan, Kuwait, Lebanon, Malaysia, Oman, Philippines, Qatar, the United Arab Emirates, the United States, and Yemen.

There previously have been cases recorded in Tunisia, Britain, France, Germany, Italy, and the Philippines.

MERS is considered a deadlier but less-transmissible cousin of the SARS virus that appeared in Asia in 2003 and infected 8,273 people, nine percent of whom died.

Like SARS, it appears to cause a lung infection, with patients suffering coughing, breathing difficulties and a temperature. But MERS differs in that it also causes rapid kidney failure.

The health experts also stressed the need to speed up investigations of the virus and to better understand the risk factors that facilitate its spread.

The closed-door WHO meeting, which took place Tuesday, was the fifth to be held on MERS with another one expected in the coming weeks, the agency said.